Oftentimes, people working in an area need to be alerted to underground hards such as power lines or pipelines. One way of doing so is to place a marker post above ground with the marker post carrying information to alert people to the hazardous underground utilities. One such marker post is shown in Schmanski U.S. Pat. No. 4,092,081 which discloses a reinforced plastic post that can be driven in the ground and still have sufficient flexibility to bend and flex if impacted by an object. Schmanski teaches the use of marker posts with glass fiber embedded in a resin core so that the combination of the glass fibers and the resin core provides both strength and flexibility to the marker post Schmanski suggests that the marker have a surface covering to protect the binder fiber combination from weather, ultraviolet rays and other adverse effects of the environment. Schmanski does not suggest painting the exterior of the marker post with a breachable coating. Still other types of marker use a fiberglass core and a UV stabilized outer wall that is molded or extruded around the fiberglass core to reduce fading and prevent glass fibers from reaching the surface.
As underground utilities are intended for extended use, the above-ground marker post should have a similar long life. To provide the needed visual awareness, the marker post needs to be have a bright color that is clearly visible against the background. In addition, the same color marker post should be used for each application. For example, a yellow marker post can be used to identify one type utility line, and a red marker post could be used to identify another type of underground hazard. These brightly colored posts visually alert those in the vicinity of the marker post to the presence of an underground hazard.
In most instance the color of the posts is mandated by the state or the industry code as it is desired to have the color of the post convey information to an observer. Consequently, it is important that the color be retained over the life of the post. Unfortunately, the present methods of providing color retention result in the color of the post fading until the color of the post takes on a whiteish color.
To provide the proper permanent color to the marker posts, a colored pigment is added to the resin used to make the marker post. Breachable coatings, such as paints, are avoided in marker posts as normal wear and tear on the marker post causes the breachable coating to flake or scratch off, resulting in loss of color to the marker post. In contrast, by adding the colored pigment to the resin, it produces a marker post that will retain its color even if the post is scratched because the pigment is located throughout the resin in the marker post. That is, by incorporating the colored pigment into the construction of the post itself as opposed to painting the post with a colored pigment, one is assured that even if the marker post is damaged, the post will maintain its original color. Consequently, relying on exterior coatings to provide a permanent color is avoided because scratches to the exterior coating destroy the original color of the post.
Although scratches to the marker post do not change the color of the marker post that have the color pigment dispersed throughout the resin, it has been found that the marker post's surface color fades due to exposure to the environment. Consequently, having the pigment located throughout the resin can fail to maintain the original exterior color of the post over an extended period of time. The surface breakdown can occur from numerous sources, but one of the most troubling sources is the environmental breakdown that results in bloom
Bloom is generally defined as a non-continuous surface coating on plastic products that comes from ingredients, such as plasticizers, lubricants, and anti-static agents, which comes out of the solution of the resin and migrate to the surface of the resin. Bloom is generally the result of gamma rays in the sunlight breaking down the molecules in the resin surrounding the glass fibers on the surface of the resin. With the evaporation of the resin in the marker post, the glass fibers are somewhat loose, and the memory retained in the glass fibers causes the fibers to propagate outward. The breakdown occurs within a few thousandths of an inch of the surface and has very little effect on the mechanical properties of the post; however, the surface appearance is noticeable as the bloom results in the post losing its original color and taking on the whitish color of the glass fibers. In addition, the migration of glass fibers leaves the marker post in a condition where anyone touching the marker post can get glass slivers.
One solution to prevent bloom on resins containing glass fibers is to use a surface mat on the exterior surface of the resin. However, while the surface mat may prevent the glass fibers from migrating to the surface, it does not prevent the resin from evaporating and changing the color of the post. That is, the polyester mat is white and once the resin evaporates, the post takes on the color of the white polyester mat. In addition, since the polyester mats are only placed on the face or back of the marker it still allows glass particles to migrate out of the edges of the posts.
The present invention provides a long life marker post that minimizes the problem of the fading of the exterior color by utilizing a pigment containing a breachable coating as the principle post color. Although the marker post resin which is located throughout the marker post contains a colored pigment dispersed throughout the resin, the colored resin becomes a secondary color that is not visible unless the outer breachable pigment containing coating is damaged. Thus, in contest with the prior art which avoids breachable pigment containing coatings on the exterior of post, the present invention relies on a breachable pigment containing coating to provide the principle color to the post and the colored resin throughout the post to provide a secondary color only in the event that there is a failure of the breachable coating.
In the present invention, the exterior surface of the marker post is coated with a non-transparent, breachable coating containing an ultraviolet-blocker that contains the same or substantially the same color pigment as the resin in the marker post. The result is a marker post with an outer breachable ultraviolet coating which blocks or inhibits the gamma rays to prevent breakdown of the resin in the post which causes the bloom that results in color loss. The outer, breachable coating extends the useful life of the marker post by preventing the post from losing its original color due to bloom. Thus, the marker post of the present invention will retain its color longer since the breachable coating on the marker post does not contain resins and glass fibers.
While the coating is described as a breachable coating, it should be understood that the breachable coating can withstand many types of impacts without breaching the coating. However, since the coating does not become an integral part, the resin contained in it can still be separated or scratched off the post if the post receives severe impacts, and for that reason is described as a breachable coating.
Thus, in the present invention, the marker post retains and relies on the original color on the exterior of the marker post. In spite of the fact that the breachable coating on the marker post is still subject to scratches and may be damaged due to subsequent impacts to the marker post, the overall color retention life of the marker post is lengthened because the breakdown of the internal color of the post occurs, if at all, only over time and over limited areas of the post.
In addition to impacts with machines or objects, the marker post is also subject to bending due to weather conditions such as wind and rain. Both of these conditions can cause localized breaching of the outer breachable coating on the marker post. Although breachable coatings such as commercial paints with ultraviolet-blockers which have long life and long color retention are commercially available, unfortunately, a single paint that has sufficient durability to adhere to the marker post and resist scratches under all types of field conditions is difficult to find. Consequently, while one coating might work in one marker post application, it might not work in another marker post application. For example, if a marker post is subjected to extreme temperatures, one type temperature-responsive coating may be useful, and if another marker post is subjected to repeated impact, another more flexible type of coating may be more suitable.
The present invention reduces the need for having a single paint coating that is responsive for each field condition by matching the field use to the paint type. For example, to have long life marker posts one selects a long life paint that contains an ultraviolet-blocking agent and has the same color pigment or substantially the same color pigment as the pigment in the resin of the marker posts. Consequently, minor damage or localized breaching of the exterior breachable coating on the marker post that can occur over time and which can result in loss of a portion of the breachable coating does not render the marker post ineffective. That is, the internal resin of the marker post carries a pigment, and the exterior breachable coating contains a pigment of the same or substantially the same color so that if the marker post is damaged, the original color will appear in the exposed area where the coating is removed. Consequently, the marker post will appear to be the same color to an observer even though portions of the breachable coating are not present.
In addition, if a protective mat or coating is used on the exterior surface of the resin and below the exterior breachable coating, the exposed portion of the marker post can still resist bloom unless the protective mat is breached. Thus, with the prevent invention, even though the marker post exterior coating is breached, the life of the marker post original color has been extended because the process of the color breakdown is inhibited through the use of a set of barriers which coact to provide a post whose color can be retained over an extended period of time.